Re: [PATCH v3] libstdc++: ppc: conditionalize vsx-only simd intrinsics

[Alexandre Oliva <oliva@adacore.com>]

On May  6, 2022, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:

> On Fri, 6 May 2022 at 17:17, Segher Boessenkool wrote:
>> > +#if defined __VSX__ || __LONG_WIDTH__ == 32
>> >  _GLIBCXX_SIMD_PPC_INTRIN(signed long);
>> >  _GLIBCXX_SIMD_PPC_INTRIN(unsigned long);
>> > +#endif
>> 
>> Is __LONG_WIDTH__ the right macro to use here?  Nothing else in
>> libstdc++v3 uses it.  "__CHAR_BIT__ * __SIZEOF_LONG__" is the usual
>> thing to do.  Is __LONG_WIDTH__ always defined anyway?

> Presumably it could be simply __SIZEOF_LONG__ == 4 if this is
> PowerPC-specific code where CHAR_BIT==8 is always true?

SGTM.  Here's the adjusted patch I'm checking in momentarily, trunk
first, then gcc-12 and gcc-11 after a week or so.  Thanks,


libstdc++: ppc: conditionalize vsx-only simd intrinsics

libstdc++'s bits/simd.h section for PowerPC, guarded by __ALTIVEC__,
defines various intrinsic vector types that are only available with
__VSX__: 64-bit long double, double, (un)signed long long, and 64-bit
(un)signed long.

experimental/simd/standard_abi_usable{,_2}.cc tests error out
reporting the unmet requirements when the target cpu doesn't enable
VSX.  Make the reported instrinsic types conditional on __VSX__ so
that <experimental/simd> can be used on PowerPC variants that do not
support VSX.


for  libstdc++-v3/ChangeLog

	* include/experimental/bits/simd.h [__ALTIVEC__]: Require VSX
	for double, long long, and 64-bit long intrinsic types.
	[__ALTIVEC__] (__intrinsic_type): Mention 128-bit in
	preexisting long double diagnostic, adjust no-VSX double
	diagnostic to cover 64-bit long double as well.
---
 libstdc++-v3/include/experimental/bits/simd.h |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/experimental/bits/simd.h b/libstdc++-v3/include/experimental/bits/simd.h
index 82e9841195e1d..b0226fa4c5304 100644
--- a/libstdc++-v3/include/experimental/bits/simd.h
+++ b/libstdc++-v3/include/experimental/bits/simd.h
@@ -2430,17 +2430,23 @@ template <typename _Tp>
   template <>                                                                  \
     struct __intrinsic_type_impl<_Tp> { using type = __vector _Tp; }
 _GLIBCXX_SIMD_PPC_INTRIN(float);
+#ifdef __VSX__
 _GLIBCXX_SIMD_PPC_INTRIN(double);
+#endif
 _GLIBCXX_SIMD_PPC_INTRIN(signed char);
 _GLIBCXX_SIMD_PPC_INTRIN(unsigned char);
 _GLIBCXX_SIMD_PPC_INTRIN(signed short);
 _GLIBCXX_SIMD_PPC_INTRIN(unsigned short);
 _GLIBCXX_SIMD_PPC_INTRIN(signed int);
 _GLIBCXX_SIMD_PPC_INTRIN(unsigned int);
+#if defined __VSX__ || __SIZEOF_LONG__ == 4
 _GLIBCXX_SIMD_PPC_INTRIN(signed long);
 _GLIBCXX_SIMD_PPC_INTRIN(unsigned long);
+#endif
+#ifdef __VSX__
 _GLIBCXX_SIMD_PPC_INTRIN(signed long long);
 _GLIBCXX_SIMD_PPC_INTRIN(unsigned long long);
+#endif
 #undef _GLIBCXX_SIMD_PPC_INTRIN
 
 template <typename _Tp, size_t _Bytes>
@@ -2450,10 +2456,11 @@ template <typename _Tp, size_t _Bytes>
     static constexpr bool _S_is_ldouble = is_same_v<_Tp, long double>;
     // allow _Tp == long double with -mlong-double-64
     static_assert(!(_S_is_ldouble && sizeof(long double) > sizeof(double)),
-		  "no __intrinsic_type support for long double on PPC");
+		  "no __intrinsic_type support for 128-bit floating point on PowerPC");
 #ifndef __VSX__
-    static_assert(!is_same_v<_Tp, double>,
-		  "no __intrinsic_type support for double on PPC w/o VSX");
+    static_assert(!(is_same_v<_Tp, double>
+		    || (_S_is_ldouble && sizeof(long double) == sizeof(double))),
+		  "no __intrinsic_type support for 64-bit floating point on PowerPC w/o VSX");
 #endif
     using type =
       typename __intrinsic_type_impl<


-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <https://stallmansupport.org>